Transforming Leftover Roast Chicken and Vegetables into a whole other meal

I roasted a chicken the other night, along with the standard root vegetables (carrots, potatoes, turnips, onions, celery, garlic cloves, etc).  It was wonderful (but everyone knows how to do this, I think, so I won't share how I did it, I'm here to talk about the leftovers).  See, the chicken (due to being sustainably raised, and my not wanting to spend a ton of money on meat) was tiny, and after the one dinner for the two of us, there wasn't really a full meal for two left for the next day.  (Also, Axel F doesn't love eating leftovers, particularly).  So to transform what was left into a new and different (and more generous) meal, I took all the meat I could off the bones of what remained of the chicken (half a breast and a thigh), chopped up all the roasted vegetables nice and small (along with some cooked broccoli I had leftover from another meal, and some thawed frozen peas) and threw together a casserole.  It turned into enough food to feed an army (or well, 8 people) generously.  This could be done meaty or vegetarian, with any kind of leftover cooked meat or vegetables that you have on hand (or if you started with drained canned tuna and frozen peas, it's the classic tuna noodle casserole).

It's basically just: cooked pasta or noodles, white sauce (bechamel) and/or cream of mushroom soup, cooked meat and/or vegetables, breadcrumbs.  And it is creamy and rich tasting (without actually packing in much fat), filling and homey, with a nice crunch from the toasty breadcrumbs.  It's what Minnesotans call "hot dish," and I love it.  If you really want to gild the lily (as our parents like to say), you could grate some cheese in before mixing it all together... but I found it plenty rich as is.

You need:
1-3 cups of cooked meat, medium dice
2-4 cups of cooked vegetables, medium dice
1 cup frozen peas, thawed under a bit of cold running water and drained
1 pound of pasta, in some kind of piece type shape - orecchiette, or farfalle, or penne, or even wide egg noodles would be great
a batch of white sauce (recipe below*) PLUS a can/carton of cream of mushroom soup** OR a double batch of white sauce made with extra seasoning***
3-4 slices of white sandwich bread (or really any bread you've got)
3-4 tbsp butter

Grease a 9 by 13 glass baking dish or similar with soft butter and set aside.  Preheat the oven to 375.

Tear up the slices of bread and add to a food processor along with 3 tbsp soft butter and a bit of salt and pepper, and pulse until the bread is in uniform crumbs and the butter is well distributed.

Prepare the white sauce* and combine it with the cream of mushroom soup.  Add enough extra milk if necessary to make the mixture loose enough - it should look about as thick as clam chowder or a spaghetti sauce.  Pour the mixture into a large bowl.

Boil the pasta or noodles in very well salted rapidly boiling water (it should taste as salty as ocean water).  Drain the pasta and add it to the white sauce in the bowl, along with your meat and/or veggies, and mix well to combine.  Taste for seasoning and add salt and pepper if necessary, and thin with more milk or some reserved pasta water if it doesn't seem saucy enough.  Now would be the time to add cheese if you want it (cheddar or even some grated parmesan would be good).  Any other seasonings you like (chopped pickled jalapenos, chopped roasted red pepper, chopped fresh herbs, etc) can be added now.

Pour the mixture into the prepared baking dish and smooth out the top.  Carefully pour on the breadcrumbs, spreading them over the whole surface.  Bake at 375 for 45 minutes to an hour, till things look bubbly and the breadcrumbs turn nice and golden brown.

*WHITE SAUCE (or, bechamel)
2 cups milk
3 tbsp butter
3 tbsp flour
bay leaf
salt and pepper

warm the milk in a saucepan on the stove, or in the microwave, in a microwave safe measuring cup.

In a larger saucepan, melt the butter.  When the foaming subsides, and with a whisk handy, sprinkle in the flour and start whisking vigorously to combine thoroughly and get rid of any bits of dry flour.  Cook this mixture (keeping it moving) for a minute or two over medium heat.  You'll smell that the raw flour scent goes away, and turns buttery and toasty.

Add the warm milk very gradually, little dribbles at a time at first, whisking as you go.  Once milk seems to outnumber the flour in the pan, you can add the rest of the milk all at once, and add the bay leaf.  Whisking constantly (being sure to get into the corners of the pan), cook until the mixture comes to a boil and thickens.  Season to taste with salt and pepper.  (Sometimes it's nice to add nutmeg to this too, especially if you're using, say, leftover cooked dark greens like kale or chard, and leftover italian sausage for the meat! mmmm.)

 **I normally would just make lots of white sauce for something like this, but I happened to have bought (on spec) a carton of condensed cream of portobello mushroom soup at Trader Joes, it seemed like it would be a tasty addition, and lo - it was!

*** if you don't use part cream of mushroom soup, in addition to doubling the amounts for the white sauce, I'd recommend amping up the flavor by adding a finely chopped onion and some garlic to the butter at the beginning, cooking it until soft and translucent but not brown, before adding the flour and continuing with the regular white sauce recipe.